Sorceror-Prophet Nalgrund:
Lords:
Drazhoath the Ashen
Just don't. He's terrible. A Sorceror-Prophet is better in every conceivable way, even has the mount option if you really badly need to be cannoned/magick'd off the table Turn 1.
Castellan - BSB, Mask of the Furnace, shield, potion of speed (goes with the HW+Shield IG unit)
Don't have to do this. Talisman of Preservation is way cheaper, doesn't take up his magic armour slot, and lets you fit in a magic weapon+enchanted item. Furnace Mask is for your Sorceror-Prophet really, he has the magic item allowance for it+another item or two.
You need a Strength-boosting weapon. Ogre Blade isn't possible (otherwise you have no ward, which is unacceptable on a BSB), but Sword of Might is cheap enough to fit in pretty easily. S4 isn't very scary, S5 puts him into the mid-tier of combat characters. You could always go great weapon, but you have to drop Speed Potion in that case.
Daemonsmith Sorcerer - Level 2, ruby ring of Ruin, Charmed shield (stands by the warmachines)
If he's Lore of Fire already, you don't need Ruby Ring. The cost of casting first your normal fireball then the bound spell is greater than just boosting your original casting. Dropping the Ring lets you take a dispel scroll, which given you don't have dispel dice printing like normal Dwarves, is a pretty good option.
Don't really need Level 2, he's only casting Fireball really, maybe Flaming Blades if he rolls it.
Infernal guard - 20 with Fireglaives
Infernal guard - 23 with musician, standard, overseer
I'd bump them both up to 25 (keep the current 23 man, but add 5 to the Fireglaives). You need a decent buffer of bodies, I2 isn't the greatest.
Magma Cannon - Hellbound
Magma Cannon - Hellbound
Eh. Magical attacks only really matter when you're faced with Ethereal. In most cases, your Sorceror-Prophet and Daemonsmith are more than capable of killing it (Fireball or Burning Wrath kills most of them pretty handily). Why jack up the price? Increased Toughness is pretty by the by, most things gunning for you don't care (Poison/massed fire/spells).
Bull Centaurs - 6 with AHW, Champion, Standard (Banner of swiftness)
Looks good. Tell us how you fair with them. They're immune to KB so Black Knights are in trouble and Grave Guard will get stomped hard if you flank attack them.
Dreadquake - Slave ogre, hellbound
Meh, nothing in their army is tough enough to warrant it, and scatter dice can always screw you. Have you considered a K'Daai Destroyer? With a bit of point shuffling you could fit one in.